This invention relates to improvements in push-pull slipsheet handlers for forklift trucks.
Load push and push-pull devices have long been used on materials handling lift trucks. Prior to the popularity of slipsheets for handling loads, some forklift trucks were equipped with load push assemblies similar to that shown in Anderson, Jr., U.S. Pat. No. 3,885,692 to push loads off of standard load-handling forks. Later, when the use of thin, flexible slipsheets came into prominence, platens having a substantially greater load-supporting surface area than standard forks were used, such as those shown in Vander Wal U.S. Pat. Nos. 3,180,513 and 3,310,189, respectively.
Still later, combination push-pull and platen assemblies were developed, such as that shown in Frees U.S. Pat. No. 4,300,867, Brudi U.S. Pat. No. 3,640,414, or those currently manufactured by Cascade Corporation of Portland, Ore. under the designations 30C and 45C. Many of these have a two-piece, or split, platen so that the platen can, at least theoretically, be inserted into the end of a standard rigid wooden pallet if it becomes necessary to handle rigid pallets as well as slipsheets. Some units, such as the aforementioned Cascade 30C and 45C devices, have transversely adjustable split platen sections capable of handling slipsheet-supported loads of different widths. Such transversely-adjustable platen sections can be either manually adjusted or hydraulically adjusted.
Other types of units have been developed featuring platens mounted on the standard forks of a truck, but for different purposes such as the swivel-type platen shown in Brennaman U.S. Pat. No. 2,957,594.
A drawback of devices such as that shown in the aforementioned U.S. Pat. No. 3,885,692, wherein a push plate is used in connection with standard, relatively narrow, pallet-handling forks, is that the forks have insufficient surface area to support loads with underlying slipsheets. Conversely, early fork-mounted platens having sufficient surface area for slipsheet handling, such as those shown in U.S. Pat. Nos. 3,180,513 and 3,310,189, are likewise unsatisfactory because they have no slipsheet pulling capability and are therefore limited to engaging a slipsheet-supported load only by knifing their platens beneath the slipsheet.
Alternatively, more modern slipsheet-handling devices such as those shown in U.S. Pat. Nos. 4,300,867 and 3,640,414, or the aforementioned CASCADE 30C and 45C push-pull devices, although quite adequate for slipsheet handling, and although employing split platens and even transversely-adjustable split platens, are most difficult to use for handling rigid pallets. This is because the platens, in order to provide the necessary supporting surface area, are so wide that a lift truck driver cannot use them to engage a rigid pallet unless he approaches the end of the pallet virtually parallel to its longitudinal dimension. Any substantial angularity in the approach makes it impossible to insert the wide platens fully into the spaces provided in the pallet. Moreover, such platens cannot engage a standard rigid pallet along one of its longer sides as standard forks can. Standard rigid wooden pallets are 40 inches by 48 inches in size and are designed to be engaged on either their ends or longitudinal sides by trucks having standard load-handling forks.
The above-described difficulties of a truck with standard forks attempting to handle slipsheets and, conversely, the difficulties of a slipsheet handler attempting to handle standard rigid pallets, have led to severe equipment problems in the materials handling industry. Many shippers of goods prefer to use slipsheets rather than rigid pallets, primarily because slipsheets are expendable and do not have to be returned. On the other hand, most warehouse establishments which receive such shipments prefer to use rigid pallets to facilitate stacking and handling of loads. Accordingly such warehouses must have at least two different types of lift trucks on hand to handle loads received from shippers: push-pull slipsheet-handling trucks to remove slipsheet-supported loads from highway trucks and transfer them to rigid pallets; and lift trucks equipped with standard load-handling forks to handle and stack the loads once they have been transferred to the rigid pallets.
This places an unduly high requirement, with respect to capital expenditures for materials handling equipment, on warehousemen and other receivers of goods, since the size of their lift truck fleets is effectively twice what it might otherwise be. Unfortunately, the lift trucks cannot be converted quickly or easily from slipsheet-handling capability to pallet-handling capability, and vice versa. This is because conversion to pallet handling requires not only removal of a complete push-pull assembly from the lift truck carriage, but also installation of standard forks, with the reverse procedure being necessary for the opposite conversion. There is insufficient time in the hectic scheduling of a warehousing operation to make such conversions repeatedly. Even where the push-pull assemblies are mounted compatibly with forks, as for example in the aforementioned U.S. Pat. Nos. 3,885,692 and 4,300,867, the push-pull assemblies are so reliant for their vertical support upon the lift-truck carriage or frame (rather than upon the upwardly-facing load-supporting surfaces of the forks) that they are substantially permanently mounted to the carriage or frame so as to be incapable of rapid attachment and detachment.